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The Spacelab 3 Atmospheric Trace Molecule Spectroscopy measurements in 1985 of stratospheric NO/NO2 abundance ratios were compared with abundance ratios calculated using a time-dependent photochemical model. A good agreement between calculated and observed values of the NO/NO2 abundance ratio was found through much of the stratosphere, indicating that the temperature-dependent rate constant K3 (NO + O3) used in the model is properly parameterized.
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The effects of heterogeneous processing by a parameterized lower stratospheric sulfate aerosol layer on model calculations were examined using a 2D photochemical model. Model results were compared with zonally averaged LIMS data on HNO3 and NO2 and in situ measurements of NO, NO(y), and ClO, taken by the ER-2 aircraft. The results obtained are contradictory: some comparisons favor heterogeneous chemistry, and some do not. It is suggested that the assumptions made to parameterize the sulfate aerosol chemistry result in a rate of heterogeneous processing that is too vigorous.
The photochemical partitioning of stratospheric odd chlorine and odd nitrogen is examined utilizing diurnal model calculations and data from the ATMOS experiment. This experiment, conducted during April-May 1985, employed a solar occultation method to obtain vertical profiles of temperature and various other trace constituents at 30 deg N and 48 deg S latitudes. The ATMOS data set confirms the presence of N2O5 in the stratosphere; however, the observed mixing ratios at sunset are more than a factor of 2 less than the calculated values. It is shown that the conversion of N2O5 into HNO3 could take place in the presence of aerosol surfaces quickly enough to affect the N2O5 mixing ratio below 30 km. Inclusion of the heterogeneous reaction brings the calculated N2O5 profile below 30 km into closer agreement with the ATMOS data.
The general objective of this research is to obtain, via remote sensing, simultaneous measurements of the vertical distributions of stratospheric temperature, ozone, and trace constituents that participate in the catalytic destruction of ozone (NO(sub y): NO, NO2, NO3, HNO3, ClONO2, N2O5, HNO4; Cl(sub x): HOCl), and the source gases for the catalytic cycles (H2O, CH4, N2O, CF2Cl2, CFCl3, CCl4, CH3Cl, CHF2Cl, etc.). Data are collected during a complete diurnal cycle in order to test our present understanding of ozone chemistry and its associate catalytic cycles. The instrumentation employed is an emission-mode, balloon-borne, liquid-nitrogen-cooled Michelson interferometer-spectrometer (SIRIS), covering the mid-infrared range with a spectral resolution of 0.020 cm(exp -1). Cryogenic cooling combined with the use of extrinsic silicon photoconductor detectors allows the detection of weak emission features of stratospheric gaseous species. Vertical distributions of these species are inferred from scans of the thermal emission of the limb in a sequence of elevation angles. The fourth SIRIS balloon flight was carried out from Palestine, Texas on September 15-16, 1986 with 9 hours of nighttime data (40 km). High quality data with spectral resolution 0.022 cm(exp -1), were obtained for numerous limb sequences. Fifteen stratospheric species have been identified to date from this flight: five species from the NO(sub y) family (HNO3, NO2, NO, ClONO2, N2O5), plus CO2, O3, H2O, N2O, CH4, CCl3F, CCl2F2, CHF2Cl, CF4, and CCl4. The nighttime values of N2O5, ClONO2, and total odd nitrogen have been measured for the first time, and compared to model results. Analysis of the diurnal variation of N2O5 within the 1984 and 1986 data sets, and of the 1984 ClONO2 measurements, were presented in the literature. The demonstrated ability of SIRIS to measure all the major NO(sub y) species, and therefore to determine the partitioning of the nitrogen family over a continuous diurnal cycle, is a powerful tool in the verification and improvement of photochemical modeling.
CoP3H14(N2O5)2H2O crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of four water molecules and two CoP3H14(N2O5)2 sheets oriented in the (0, 1, 0) direction. In each CoP3H14(N2O5)2 sheet, Co3+ is bonded to four N3- and two O2- atoms to form CoN4O2 octahedra that share corners with two PO4 tetrahedra. There are a spread of Co–N bond distances ranging from 1.97–2.09 Å. There are one shorter (1.99 Å) and one longer (2.02 Å) Co–O bond lengths. There are three inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one CoN4O2 octahedra and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedral tilt angles are 31°. There are a spread of P–O bond distances ranging from 1.52–1.62 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There is two shorter (1.50 Å) and two longer (1.64 Å) P–O bond length. In the third P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one CoN4O2 octahedra and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedral tilt angles are 39°. There are a spread of P–O bond distances ranging from 1.51–1.63 Å. There are four inequivalent N3- sites. In the first N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one Co3+ and three H1+ atoms. There is two shorter (1.02 Å) and one longer (1.03 Å) N–H bond length. In the second N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one Co3+ and three H1+ atoms. There are a spread of N–H bond distances ranging from 1.02–1.04 Å. In the third N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one Co3+ and three H1+ atoms. There is one shorter (1.02 Å) and two longer (1.03 Å) N–H bond length. In the fourth N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one Co3+ and three H1+ atoms. There are a spread of N–H bond distances ranging from 1.02–1.04 Å. There are fourteen inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the ninth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the tenth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the eleventh H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the twelfth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the thirteenth H1+ site, H1+ is bonded in a distorted linear geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.63 Å) H–O bond length. In the fourteenth H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.04 Å) and one longer (1.51 Å) H–O bond length. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one P5+ and one H1+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Co3+ and one P5+ atom. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to one Co3+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a bent 120 degrees geometry to one P5+ and one H1+ atom. In the fifth O2- site, O2- is bonded in a bent 120 degrees geometry to one P5+ and one H1+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two P5+ atoms. In the seventh O2- site, O2- is bonded in a single-bond geometry to one P5+ atom. In the eighth O2- site, O2- is bonded in a single-bond geometry to one P5+ atom. In the ninth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the tenth O2- site, O2- is bonded in a bent 120 degrees geometry to one P5+ and one H1+ atom.
It is now clear that heterogeneous reactions play an important role in controlling the concentration of ozone in the stratosphere. In this work, the loss of N2O5 on ice substrates has been studied in a flow reactor in an attempt to gain a more fundamental understanding of these reactions. The apparent reaction probability in this system was found to decrease as the substrate was exposed to N2O5. A model which corrected for the loss of surface sites was developed and although it appears to fit the data for a given experiment quite well, it is concluded that the loss of reactive sites is not the full explanation. In addition, the results of an experimental and modeling study suggest that reaction on the internal surface of the ice substrates is not a major loss mechanism for N2O5 in the current work.
A three-dimensional off-line chemistry transport model, driven by European Center for Medium-Range Forecasts winds and temperatures, is used to interpret measurements of NO and NO2 taken from the DC-8 during the second Airborne Arctic Stratospheric Expedition. The model was run in three configurations: gas phase chemistry alone, inclusion of the N2O5 aerosol reaction, and inclusion of both N2O5 and ClONO2 aerosol reactions. The run including the N2O5 aerosol reaction alone usually agreed best with measured NO(x)/NO(y) ratios in midlatitude air masses. The NO(x)/NO(y) ratios of the run with both aerosol reactions were always too low, while the gas phase ratios were usually too high, especially during March. All three simulations generated extremely low NO2/NO(y) ratios in air parcels that had spent several days or more in the polar night. Measured NO2/NO(y) ratios in these types of air masses were sometimes equally low but could also be considerably higher. Observed NO/NO2 ratios differed strongly from known theory.
Nitric oxide (NO) is emitted in large quantities from coal-burning power plants. During the day, the plumes from these sources are efficiently mixed into the boundary layer, while at night, they may remain concentrated due to limited vertical mixing during which they undergo horizontal fanning. At night, the degree to which NO is converted to HNO3 and therefore unable to participate in next-day ozone (O3) formation depends on the mixing rate of the plume, the composition of power plant emissions, and the composition of the background atmosphere. In this study, we use observed plume intercepts from the Wintertime INvestigation of Transport, Emissions and Reactivity (WINTER) campaign to test sensitivity of overnight NOx removal to the N2O5 loss rate constant, plume mixing rate, background O3, and background levels of volatile organic compounds using a 2-D box model of power plant plume transport and chemistry. The factor that exerted the greatest control over NOx removal was the loss rate constant of N2O5. At the lowest observed N2O5 loss rate constant, no other combination of conditions converts more than 10 percent of the initial NOx to HNO3. The other factors did not influence NOx removal to the same degree.
Upper atmospheric research programs in the department of chemical kinetics are reported. Topics discussed include: (1) third-order rate constants of atmospheric importance; (2) a computational study of the HO2 + HO2 and DO2 + DO2 reactions; (3) measurement and estimation of rate constants for modeling reactive systems; (4) kinetics and thermodynamics of ion-molecule association reactions; (5) entropy barriers in ion-molecule reactions; (6) reaction rate constant for OH + HOONO2 yields products over the temperature range 246 to 324 K; (7) very low-pressure photolysis of tert-bytyl nitrite at 248 nm; (8) summary of preliminary data for the photolysis of C1ONO2 and N2O5 at 285 nm; and (9) heterogeneous reaction of N2O5 and H2O.
LIMS, SAMS, SBUV and in-situ data have been used to infer species not measured but which are of photochemical interest, e.g., O(3P), O(1D), NO, N2O5, OH, HO2, ClO and HCl. (LIMS = limb infrared monitor of the stratosphere; SAMS = stratospheric and mesospheric sounder; and SBUV = solar backscattered ultraviolet instrument.) Production and loss of odd nitrogen have been calculated and estimates have been made of the odd nitrogen transport due to adiabatically driven circulation derived from LIMS data. Data used from LIMS include O3, NO2, HNO3, H2O and T. CH4 and N2O were taken from SAMS and the UV solar flux from the SBUV instrument. Species were inferred for periods in October, December, March and May. Results for December are discussed. Results indicate: (1) maximum stratospheric odd nitrogen levels of 25 ppbv; (2) evidence of odd nitrogen transport from the mesosphere appearing at 25 km in the wintertime polar latitudes; (3) the polar night build-up of high levels of N2O5 beginning after the autumnal equinox; and (4) the possibility of large downward fluxes of odd nitrogen into the troposphere during the winter at latitudes poleward of 60 degrees.
A detailed model of polar stratospheric clouds (PSCs), which includes nucleation, condensational growth. and sedimentation processes, has been applied to the study of heterogeneous chemical reactions. For the first time, the extent of chemical processing during a polar winter has been estimated for an idealized air parcel in the Antarctic vortex by calculating in detail the rates of heterogeneous reactions on PSC particles. The resulting active chlorine and NO(x) concentrations at first sunrise are analyzed with respect to their influence upon the Antarctic ozone hole using a photochemical model. It is found that the species present at sunrise are primarily influenced by the relative values of the heterogeneous reaction rate constants and the initial gas concentrations. However, the extent of chlorine activation is also influenced by whether N2O5 is removed by reaction with HCl or H2O. The reaction of N2O5 with HCl, which occurs rapidly on type 1 PSCs, activates the chlorine contained in the reservoir species HCl. Hence the presence and surface area of type 1 PSCs early in the winter are crucial in determining ozone depletion.
The study presents a model that incorporates the physics and physical chemistry of ice surfaces relevant to polar stratospheric clouds. Surface concentrations of H2O, HCl, HOCl, ClONO2, and N2O5 on ice and nitric acid trihydrate (NAT) crystals are computed, and surface reaction rates and reaction probabilities (sticking coefficients) are determined. For gas pressures of about 10 exp -7 torr and temperatures in the range of 180-200 K, HCl completely coats ice and water-rich NAT surfaces, while HOCl, ClOHO2, and N2O5 may cover 0.01-1 percent of these surfaces. The energy parameters are used to calculate surface temperatures such as adsorption and desorption constants, surface coverages, reaction rate coefficients, surface diffusion coefficients, and reaction probabilities for various species and chemical interactions on ice and NAT surfaces. Implications for chemical processing on polar stratospheric clouds are discussed.
We have used a time series of aerosol surface based on the measurements of Hofmann to investigate the modulation of total column ozone caused by the perturbation to gas phase chemistry by the reaction N2O5(gas) + H2O(aero) yields 2HNO3(gas) on the surface of stratospheric aerosols. We have tested a range of values for its reaction probability, gamma = 0.02, 0.13, and 0.26 which we compared to unperturbed homogeneous chemistry. Our analysis spans a period from Jan. 1974 to Oct. 1994. The results suggest that if lower values of gamma are the norm then we would expect larger ozone losses for highly enhanced aerosol content that for larger values of gamma. The ozone layer is more sensitive to the magnitude of the reaction probability under background conditions than during volcanically active periods. For most conditions, the conversion of NO2 to HNO3 is saturated for reaction probability in the range of laboratory measurements, but is only absolutely saturated following major volcanic eruptions when the heterogeneous loss dominates the losses of N2O5. The ozone loss due to this heterogeneous reaction increases with the increasing chlorine load. Total ozone losses calculated are comparable to ozone losses reported from TOMS and Dobson data.
A novel cryogenic Fourier transform spectrometer (FTS) has been developed for limb emission measurements in the mid IR-region from balloon-borne platforms. The FTS is a rapid scanning interferometer using a modified Michelson arrangement which allows a spectral resolution of 0.04 cm(exp -1) to be achieved. Solid carbon-dioxide cooling of the spectrometer and liquid-helium cooling of the detectors provide adequate sensitivity. The line of sight can be stabilized in terms of azimuth and elevation. A three-mirror off-axis telescope provides good vertical resolution and straylight rejection. Calibration is performed by high elevation and internal blackbody measurements. Four balloon flights were performed, two of them during spring turn-around 1989 and 1990 over mid-latitudes (Aire sur L'Adour, France, 44 deg N) and two near the northern polar circle in winter 1992 (Esrange, Sweden, 68 deg N). Limb emission spectra were collected from 32 km to 39 km floating altitudes covering tangent heights between the lower troposphere and the floating altitude. The trace gases CO2, H2O, O3, CH4, N2O, HNO3, N2O5, ClONO2, CF2Cl2, CFCl3, CHF2Cl, CCl4, and C2H6 have been identified in the measured spectra. The 1989 data have been analyzed to retrieve profiles of O3, HNO3, CFCl3 and CF2Cl2. The flights over Kiruna have provided the first ever reported profile measurements of the key reservoir species ClONO2 and N2O5 inside the polar vortex.
This paper presents time-dependent simulations of the response of the stratosphere to the injection into the atmosphere of massive amounts of sulfur during the eruption of Mt. Pinatubo (The Philippines) in June 1991. The study is based on a coupled two-dimensional chemical-dynamical-radiative model to which a microphysical model for sulfate aerosol formation and fate has been added. The study suggests that, during the first year (July 1991 to June 1992) following the volcanic eruption, the observed changes in the ozone amount integrated between 65 deg S and 65 deg N were caused primarily by changes in the meridional circulation (associated with heating by the volcanic cloud in the tropics) and in the photolysis rate of molecules such as ozone (associated with backscattering of light by the cloud). During the second year after the eruption, as the aerosol was dispersed at all latitudes and, in particular, reached the polar region, the largest contribution to ozone reduction resulted from the heterogeneous chemical conversion of N2O5 and ClONO2 on the surface of the aerosol particles. The conversion of the latter compound, and hence the magnitude of the calculated ozone depletion, is highly dependent on the temperature in the lower stratosphere. Despite the fact that the surface area provided by aerosol particles decreased during the second year following the eruption, the calculated ozone depletion remained significant because the conversion of N2O5 is insensitive to the aerosol surface area density for values larger than 1-10 sq microns/cu cm (depending on latitude). The predicted reduction in ozone at 20 km in March during the third year (July 1993 to June 1994) of the model integration is smaller by a factor of 2 than it was during the second year.
Extensive airborne measurements of the reactive nitrogen reservoir (NOY) and its component nitric oxide (NO) have been made in the lower stratosphere. Box model. simulations that are constrained by observations of radical and longlived species and which include heterogeneous chemistry systematically underpredict the NO(x) (= NO + NO2) to NOY ratio. The model agreement is substantially improved if newly measured rate coefficients for the OH + NO2 and OH + HNO3 reactions are used. When included in 2-D models, the new rate coefficients significantly increase the calculated ozone loss due to NO(x) and modestly change the calculated ozone abundances in the lower stratosphere. Ozone changes associated with the emissions of a fleet of supersonic aircraft are also altered. phase chemistry linking NO(x) and nitric acid (HNO3), which is generally the most abundant NOY species. Because the continuous daylight present at summer high latitudes limits the heterogeneous production of HNO3 by N2O5 hydrolysis, gas-phase reactions primarily control the balance between NO(x) and NO(y). Outside summer polar regions, the N2O5 hydrolysis reaction occurring on stratospheric sulfate aerosols is a more important sink of NO(x), particularly in the lower stratosphere during winter when heterogeneous pathways account for most of the HNO3 production.